Pumps for pumping liquids and other materials at very high pressures are well-known in the art and have been used for decades in a wide range of applications. Generally speaking, pumps capable of pumping liquids at pressures greater than about 4,000 pounds per square inch gauge (psig) are referred to in the art as "intensifier pumps," although the usage is somewhat inconsistent and may or may not be used to describe pumps capable of pumping liquids at or above the foregoing pressure.
Generally speaking, most high pressure or intensifier pumps are used in the final stage of a multi-stage pumping system in which one or more low and/or intermediate pressure pumps may be operated in successive stages to pre-pressurize the material before it is fed to the high pressure intensifier pump. The high pressure intensifier pump then increases the pressure of the material to the final desired high pressure.
A typical high pressure intensifier pump may comprise a piston mounted for reciprocation within a bore or cylinder. As the piston moves back and forth within the cylinder, the material being pumped is alternately drawn into the cylinder via the pump inlet and then compressed by the piston. The pressurized material is then discharged via the pump outlet. The piston may be reciprocated by any of a wide range of systems and devices well-known in the art for such purposes. For example, the piston may be reciprocated by a cam or crank type of actuator (i.e., by mechanical means) or by a hydraulic pump. If a hydraulic pump is used to reciprocate the piston, the hydraulic pump may comprise a separate or integral component of the high pressure intensifier pump. In one commonly used configuration, the hydraulic pump comprises an integral portion of the high pressure pump, with one end of the high pressure piston being connected directly to the hydraulic piston. The surface or face area of the hydraulic piston is selected so that it is greater than the surface or face area of the high pressure piston. Consequently, hydraulic fluid under a relatively low pressure will be capable of moving the high pressure piston against the material being pumped to produce the high pressure discharge. Indeed, it is not uncommon for intensifier pumps having the foregoing configuration to pump materials at pressures in excess of 60,000 psig with hydraulic fluid pressures of only about 3,000 psig.
While high pressure intensifier pumps of the type described above are being used, they are not without their disadvantages. For example, it is often difficult to provide an effective and reliable seal for the high pressure piston, particularly if the pump is used to pump cryogenic materials, such as liquid nitrogen or liquid oxygen. First, the material used to seal the space between the piston and cylinder must be capable of withstanding without failure the low temperatures associated with such cryogenic materials. Second, the different thermal expansion coefficients of the various materials comprising the many components of the pump (e.g., the piston, piston seal, and cylinder) can result in the formation of relatively large gaps or clearances between the components. For example, when subjected to low temperatures, the piston seal may shrink more rapidly than the piston and cylinder. If the shrinkage is excessive, the seal may no longer effectively seal the gap between the piston and cylinder. While pumps have been developed which are suitable for pumping such low-temperature or cryogenic materials, the seal arrangement and material comprising the seal often precludes the pump from being used to pump other materials or operate at higher temperatures.
A similar situation exists with respect to the pressure ranges within which the pump is to operate. For example, a pump design suitable for intermediate pressure ranges is often not suitable for use at higher pressures and vice-versa.
The foregoing limitations on the temperature and pressure ranges allowable with a given pump design typically mean that different pumps must be used depending on the particular application. Besides requiring a wide inventory of pumps, such a circumstance also precludes the option of using a single pump or a single pump design in more than a few different applications.